<!doctype html>
<meta charset="utf-8">
<style>
  .flex {
    display: flex;
    flex-direction: column;
  }
  .grid {
    display: grid;
    flex-basis: 20px;
    border: 1px solid;
  }
</style>
<div class="flex">
  <div class="grid">
    <div style="height: 50px;"></div>
  </div>
</div>
